塔里木盆地喀什凹陷克拉托天然气来源分析及聚气特征

塔里木西南喀什凹陷的克拉托天然气主要表现为原油的溶解气或者湿气,甲烷含量为74.59%~85.58%,克4井和克30井天然气则为较干的湿气。克拉托天然气的δ¹³C₁值为-41.2‰~-40.6‰,δ¹³C₂值为-30.0‰~-27.4‰。气源对比表明克拉托天然气主要源自具有混源母质特征的中侏罗统湖相烃源岩,不同于源自石炭系烃源岩的阿克莫木天然气。喀什凹陷的中-下侏罗统烃源岩主要是由于新近系的巨厚沉积才从未成熟—低成熟阶段进入成熟—高成熟阶段,生成的油气在克拉托背斜圈闭中聚集,虽也属晚期成藏,却具有连续聚气的特征。上新世末期,喀什凹陷的周缘开始抬升,早期油气藏受到破坏,形成了现今的地表油气苗或油砂。

SOURCE AND GATHERING FEATURES OF KELATUO NATURAL GAS IN THE KASHI SAG, TARIM BASIN

The Kelatuo nature gas in the Kashi Sag, southwestern Tarim Basin, was mainly composed of crude oil dissolved gas, or wet gas, with methane content ranging from 74.59% to 85.58%, where only the nature gas of the Wells Ke 4 and Ke 30 was wet gas with a little leaning to dry. The ¹³C₁ values ranged from -41.2‰ to -40.6‰, and δ¹³C₂ values from -30.0‰ to -27.4‰ for the Kelatuo gas. The comparison between the gas and source rocks showed that the Kelatuo gas might be mainly derived from lacustrine source rocks of the Middle Jurassic Yangye Formation, which was different from the Akemo natural gas generated by Carboniferous source rocks in the Kashi Sag. The hydrocarbon-generating history indicated that the Jurassic source rocks in the Kashi Sag became mature-high mature from immaturity because of huge deposits of the Neogene, and the generated oil and gas gathered in the Kelatuo anticline traps. The hydrocarbon accumulation process should be so called "late hydrocarbon accumulation", with the character of continuous gas gathering. By the end of Plioence, the peripheral mountains of the Kashi Sag began to rise, which resulted in the destruction of early reservoir and forming the present oil and gas seeps or oil sandstones.